The present invention is directed to a semiconductor component, particularly of silicon, with a sensor or actuator monolithically integrated therein.
The monolithic integration of a thermal sensor together with electronic circuits for the drive or, respectively, evaluation on a silicon wafer and the simultaneous manufacture of the integrated components in a standard process yields considerable advantages with respect to functional properties, dependability, miniaturization and simplification of the manufacture of these components. Thermal sensor such as, for example, temperature sensors, thermal mass flow sensors and thermal radiation sensors and actuators such as, for example, heating elements must be optimally thermally insulated from the substrate of the component in order to minimize both the heat capacity as well as the thermal conductivity to the substrate. This is necessary in order to minimize the response time of the sensor elements and to maximize the sensitivity thereof. Moreover, the quantity of heat required for a specific temperature difference should be reduced.
Previous proposals for the thermal insulation of sensors in semiconductor components with circuits monolithically integrated therein make use of methods of bulk micromachining. A gas flow sensor wherein aluminum-polysilicon thermocouples utilizing the Seebeck effect are integrated together with CMOS circuits are disclosed in the publication by D.Moser et al., "Silicon Gas Flow Sensors Using Industrial CMOS and Bipolar IC Technology" in Sensors and Actuators A,25-27, 577-581 (1991). In the manufacture of this component, the silicon substrate is removed selectively relative to the sensor layers with an anisotropic etching from the front side. Deep holes or trenches arise in the silicon substrate as a result thereof. Given the mass flow sensor disclosed in the publication by E.Yoon et al., "An Integrated Mass Flow Sensor with On-Chip CMOS Interface Circuitry" in IEEE Trans. on Electr. Dev. 39, 1376-1386 (1992), the substrate is etched out proceeding from the back side. The thermal sensors then lie on a membrane of, for example, oxide or silicon nitride on the chip surface and are then thermally coupled to the substrate only via this membrane. Special mounting techniques are required due to the structuring of the back side.
When etching from the front side, the sensor elements are usually realized as bridges or cantilevers that span the etched holes or recesses or, respectively, project into these. The thermal insulation of the sensors ensues via the surrounding medium (for example, nitrogen) and the usually thin suspensions of the bridges or cantilevers. The deep holes or trenches in the substrate can be very easily contaminated by particles. These particles, for example, are entrained by the gas flow in flow-through sensors.